This is a FIRST award proposal to investigate relational learning in subject's with mental retardation. Such learning is essential to independent human functioning. A hierarchy of three relational discrimination skills will be studied: arbitrary matching, arbitrary matching learning set, and emergent arbitrary stimulus relations (Sidman equivalence). The first aim is to study arbitrary matching and arbitrary matching learning set in subjects who are initially unable to acquire arbitrary relations without highly structured teaching,procedures. The studies will follow-up on findings that procedures designed to facilitate acquisition of arbitrary matching by training skill components can be adapted to promote rapid trial-and-error learning. This extension of the learning set outcome to relational discrimination will extend the generality of an important set of observations that previously have been made primarily with simple discrimination. Subjects with varying degrees of retardation will be included to extend earlier research that indicated a relation between level of retardation and learning set formation. The second aim is to investigate "emergent" matching performances in subjects with low mental ages (MA). The emergent performances investigated will be those identified by Sidman and Tail by (1982), as indicating that arbitrary matching relations are relations of meaning, or equivalence relations. it is likely that many subjects will initially not show these capacities. The studies will test the prediction of relational frames theory that the provision of a history of trained symmetric and transitive performances will be sufficient to produce emergent symmetry and transitivity. Such emergent performances have been considered an integral part of linguistic and symbolic behavior. Little is known about the mechanisms of their development, however, perhaps because they occur so readily in normally developing humans. The studies will contribute to an understanding of retardation and its remediation.